This invention is related to ski goggles or the like and is more particularly concerned with an improved construction which is useful under differing ambient light conditions.
Skiing has become recently a major winter sports activity for increasing numbers of people of all ages. Ski goggles perform a dual function for the skier. Firstly, the ski goggles provide a shield in front of the eyes to protect the eyes from the wind and thereby prevent tearing. Tearing obstructs vision and is dangerous to the skier. Secondly, the ski goggle is fitted, in most instances, with a lens formed of a material which is absorbent to light.
The greatest quantity of ski goggles sold at the present time are provided with two sheets of colored filter material which may be switched manually by the skier to provide accommodation for different ambient light conditions which occur during various portions of the day. Usually, a dark colored filter is placed in the goggle frame for bright sunshine during the middle part of the day. The dark colored filter used for bright sunlight is usually a neutral grey or green color and has a visual transmittance on the order of 10% to 20%. Normally, a yellow filter is used in the diffuse light which occurs in the later part of the afternoon or in shaded areas. For this more diffuse lighting, the yellow filter is used to permit better visibility of surface variations of the ski slope.
Ski goggles have been proposed in the past with a photochromic composition included in the lens. These ski goggle lenses are intended to change color under the influence of sunlight, particularly the ultraviolet wavelengths of light.
Photochromic compounds change color on exposure to and/or withdrawal from specific types of electromagnetic radiation. The known compounds that are reversible, i.e., change from one color to another under the influence of certain electromagnetic radiation and change back to the original color in the absence of that electromagnetic radiation have found use in very few practical applications. Usually, the electromagnetic radiation is light in the ultraviolet portion of the electromagnetic spectrum. The impracticality is largely due to the limited useful life of the compounds. To be satisfactory in ski goggles, these compounds must react quite rapidly to the activating radiation and they must have a reasonable useful life.
It is known that, in general, a photochromic reaction is produced by a photochromic substance which contains bi-stable atoms and/or molecules which are capable of changing back and forth between two distinct energy states. Generally, the changes between the different states are induced by absorbed radiant energy and the differences of state may be different atomic, molecular, or electronic configurations.
The few ski goggles available having a photochromic composition included therein, however, have been poorly accepted as the useful life of these goggles is extremely limited. In one case, goggles have been proposed using a liquid solution of the photochromic composition, which is, of course, not at all satisfactory in an active sport such as skiing and particularly in very cold weather. Other ski goggles previously available have had a very limited life, and generally a very slow response for the photochromic reaction. As the goggles aged, the reaction time becomes longer and longer.
The production of satisfactory photochromic filters for ski goggles and other purposes has been a continuing problem, mainly because of the very limited useful life of the chemicals involved in the photochromic reactions. A few inorganic compounds are known to be fairly resistant to breakdown upon continual color change reactions; however, such compounds react too slowly to provide satisfactory photochromic ski goggle filters. Some metallo-organic compounds have been satisfactory with respect to the time of return factor; however, the incorporation of these materials in the filter support has presented many problems. Most of such compounds perform their reactions quite well in solutions, but when incorporated in a solid their effectiveness is reduced appreciably. Furthermore, to be a potentially useful photochromic compound for use in ski goggles, the absorption characteristics of the two energy states must closely match the requirements of the application, i.e. the absorption characteristics must be quite different and in particular portions of the electromagnetic spectrum.